Method of making dental casting patterns



0a. 6, 1970 E, KOPP v 3,532,776

METHOD OF MAKING DENTAL CASTING PATTERNS Filed Dec. 16, 1965 2Sheets-Sheet 1 IN VENTOR Eric/Z Kopp ATTORNEYS METHQD' 0F MAKiNG DENTALCASTING PATTERNS 2 SheetsSheet 2 Filed Dec. 16, 1965 INVENTOR Eric 7 K0ATTORNEYS United States Patent C) Int. Cl. A61c 13/08; B 22c 7/02; B29c1/02 US. Cl. 264-19 15 Claims ABSTRACT OF THE DISCLOSURE This disclosureprovides a method for making dental castings which have a thin wallthiickness in at least a portion thereof. A dental die model of at leastone tooth form from an individual and a sheet of thermoplastic materialare provided. The sheet of thermoplastic material is heated and thesoftened sheet is conformed to the dental die model thereby forming anaccurate reproduction thereof. The material in the reproduction is thencooled to form the thermoplasic material into a shaped dental castingpattern. The dental casting pattern is embedded in a molding means andsubsequently removed to form a mold cavity therein. Molten metal ispoured into the molding means to form a dental casting in the moldcavity. The conforming step may include the step of effecting adifferent air pressure on each side of the sheet to fit over the dentaldie model to aid in the formation of the accurate reproduction thereof.The conforming step may also include the step of mechanically stretchingthe softened sheet of thermoplastic material over the dental die modelby an amount effective to avoid formation of folds therein.

BACKGROUND OF THE INVENTION The present state of dentistry requires everfiner and more intricately shaped casting patterns for the manufactureof crowns, bridges, cast clasps and the like. In most instancesextremely thin wall thicknesses are, at least locally, involved which,for example, on the labial side of facing crowns may be only about 0.2mm.

Such casting patterns have hitherto been made of wax in a time-consumingmanual operation which may be carried out, for example, by heating anappropriately thin sheet of wax over a flame and then pressing it onto apattern support or dental die model, exg. the pattern of a tooth stump,or form from an individual, or by repeatedly immersing the patternsupport or dental die model in molten wax.

In both cases a wax cap is obtained as a basic pattern which is tocorrespond to the thinnest portion of the casting pattern, and on thiswax cap then the remaining part of the pattern, e.g. the remaining crownwall up to the cutting edge or the like, is alsobuilt up in wax, and, ifrequired, retention means for a front facing of plastics or porcelain orthe like are provided.

In this operation it is difficult to achieve thin wax walls of constantwall thickness, to avoid spots or portions which result too thinunintentionally, and, above all, to remove the wax pattern undamagedfrom the pattern support so that it can subsequently be embedded andcast in metal. It happens only too often that parts of the delicate waxform are deformed or broken or that the entire pattern is destroyedaltogether. The whole timeconsuming operation then has to be repeated.

The same applies, similarly, to the so-called telescopic crowns in whichmost accurate parallelism of the outer walls of the inner crown and theinner walls of the outer crown is the important thing. In this case,too, the pattern 3,532,776 Patented Oct. 6, 1970 is formed of wax on atooth stump pattern serving as pattern support. Subsequently, the modelstump is inserted in the parallelometer together with the wax cap andthe surplus wax is removed by moving the doctor blade of theparallelometer therearound. It is extremely difficult to maintain therim of the inner crown in the region of the tooth neck in the requiredwall thicknes of about 0.2 mm. This rim results either too thick, thenthe crown will be too thick in the zone of the gums, or too thin andwill be broken away when the wax cap is pulled off or it will be scrapedthrough and the pattern is useless. Generally, this pulling off isparticularly critical because the slightest deformation will cause theloss of parallelism.

It will be readily appreciated that this operation using a wax patternis very time-consuming.

SUMMARY OF THE INVENTION The present invention provides a method ofmaking dental casting patterns which comprises the steps of mechanicallyapplying a previously plasticized pattern foil or sheet of plastics to apattern support for making a basic pattern of uniform wall thickness,said pattern support being the model of a tooth stump or the like andsaid pattern sheet having a thickness corresponding to the thinnest spotof a casting pattern to be made, severing said basic pattern aftercuring from the remaining part of said pattern sheet, embedding saidbasic pattern, and casting said basic pattern.

In certain cases it will be found expedient to effect the casting of thebasic pattern only after previous application of wax to portions of saidbasic pattern which correspond to thicker portions of said castingpattern.

The casting itself is effected in a known manner by metal casting.

In a more specific embodiment of the invention, the application of theplastics pattern foils or sheets produces results particularlyadvantageous and simple when realiz'ed in a manner known per se bycompressed air. In certain cases, especially where simple shapes areinvolved, it is also possible to work with a vacuum. It is emphasizedhowever, that the specific use of compressed air and/ or vacuum in theformation of dental casting patterns of the type contemplated by thisinvention has not heretofore been known in the prior art.

A casting pattern made by this method reliably has a minimum wallthickness corresponding to the chosen sheet, the parts additionallymodeled on in wax having a rigid carrier so that any risk of fracture isprecluded. The basic pattern is easily removable from the support.

The method of one of the embodiments of the invention preferablly usesplastics which burn in the mold without leaving residues, such aspolymethacrylates, polyolefines and the like.

It is self-evident that the method of the invention is not only suitablefor facing and telescopic crowns, which have been mentioned by way ofexample, but for almost all casting work occurring in dentistry. Evenwhen making cast metal saddles, clasps, bands, Wires, skeleton orrationed dental plates as well as total dental plates, the castingpatterns according to my novel method can be made of plastic foils orsheets.

Since the basic pattern formed of the plastics pattern sheet will shrinkafter forming, and that in a higher degree than the hitherto customarywax pattern, so that in most cases such shrinkage can no longer becompensated in the usual manner by means of a more strongly expandingembedding compound, according to a further feature of the invention acompensating sheet of plastics material having a thickness correspondingto the shrinkage to be compensated may be applied, mechanically, priorto forming, directly and accurately fitting to the surface of the objectto be formed. Preferably, this is so effected that the compensatingsheet, prior to the forming, is applied to the surface of the patternsheet facing the object to be formed and then plasticized and applied tothe object together with the pattern sheet.

For the compensating sheet a synthetic material is chosen which iseasily deformable, preferably has a somewhat lower melting point thanthe pattern sheet and, above all, does not combine with the latter, sothat the compensating sheet can be easily removed after the formingoperation.

When choosing the thickness of the compensating sheet, also theshrinkage of the casting should preferably be considered to ensureaccurately fitting dimensions of the finished casting.

As materials for the pattern sheet and the compensating sheetpolyethylene and polystyrene respectively, may be chosen, for example.

BRIEF DESCRIPTION OF DRAWINGS The above-described method can be carriedout analogously by different devices. A particularly expedient devicefor this application will be hereinafter described by way of example andwith reference to the accompanying drawings, in which:

FIG. 1 is a side elevational view of the device according to theinvention;

FIG. 2 is a view similar to FIG. 1, with parts broken away and showingthe upper structure of the device turned through 180 with respect toFIG. 1;

FIG. 3 is a vertical section through a detail of the device;

FIG. 4 is a top plan view of the same detail, and

FIG. 5 is a sectional view of basic patterns produced by the device ofFIGS. 1 and 2.

DESCRIPTION OF SPECIFIC EMBODIMENTS With reference to FIGS. 1 and 2, theapparatus which is particularly suitable for carrying out the method ofthe invention comprises a base 1 with a working table 2 including a tray3 for receiving pattern supports, such as tooth stump patterns 4 (FIGS.3 and 4) or the like, which serve to make a basic pattern 5 (FIG. 5) ofthe final casting pattern.

Pillars 6 on the working table 2 carry axially slidable thereon asupporting plate 7 for a plastics pattern foil or sheet 8 (FIG. 3) whichcan be secured in place by means of a vertically pivotable clampingframe 9 to be fixed in its operative or clamping position by a lockinglever 10.

A column 11 extending upwardly from the base 1 adjacent the workingtable 2 carries a rotary head 12 provided with an arm .13 carrying atone end thereof a heater 14, such as an infrared radiator or a hot airsource or the like, and with another arm 15 carrying a pressure cylinder16 with a blower head 17. The heater 14 and the blower head 17 canalternately be brought in a position above the supporting plate 7 withthe sheet 8. The pressure cylinder 16 accommodates a piston or adiaphragm respectively, not shown, unilaterally acted upon, forinstance, in the working direction, i.e. from above, by compressed airand arranged to move the blower head 17, which is influenced by a returnspring, through its operative stroke.

The apparatus operates as follows:

The pattern support, e.g. tooth stump pattern 4, which the castingpattern is to be made to conform to has an extension 4a which need notbe copied and by which it is embedded in plaster or plasticine oranother kneadable or plastic compound 21 in the tray 3. The latter hasthe advantage that, unlike plaster, it involves no curing time and canbe reused. The tray 3 is preferably made to be interchangeable so thatafter each working cycle it can be replaced by another one which hasbeen prepared in the meantime. Such embedding is preferably effected soas to make the embedding compound flush with the upper edge of the tray3, with the tooth stump pattern 4 projecting upwardly therefrom. Vents(not shown) may be provided in the bottom of the tray 3.

Upon insertion of the tray 3 in the working table 2 and after havingclamped to the supporting surface 7 a plastics pattern foil or sheet,such as the sheet 8, of a thickness corresponding to the wall thicknessof the final casting pattern where this is thinnest, the heater 14 ispositioned above the sheet, as shown in FIG. 2. As soon as the sheet hassufiiciently been plasticized by the heat, the heater 14 is replaced bythe pressure cylinder 16 in that the rotary head 12 is rotated by meansof a lever 22. When compressed air is admitted to the pressure cylinderfrom a supply, this causes the blower head 17 to descend onto theclamping frame 9 for the sheet and move on down, taking along the sheetand its supporting plate 7 against the action of springs 18 on thepillars 6 until the supporting plate 7 abuts against a shoulder 3a ofthe tray 3 so that the sheet comes to lie at the level of the upper rimof the tray 3 and the pattern support 4 to be copied projects into afront-end recess 19 in the blower head forming a pressure chamber.During the last part of its downward movement, the sheet is stretchedforward over the support 4 according to the projecting height of thelatter, whereby any formation of folds is avoided and uniform wallthickness is attained as soon as compressed air is introduced into therecess 19 of the blower head 17 to effect a different air pressure oneach side of the sheet and press the sheet tightly around the patternsupport which is thus copied with an accuracy determined by the adjustedpressure of the compressed air.

After the formed sheet or the like has cooled down, the blower head 17is evacuated through an appropriate conduit and is restored, as well asthe supporting plate 7, into its upper position by spring action,whereby the sheet is removed from the support. Upon unlocking of theclamping frame 9 the sheet is detached and the shaped part thereof,which forms a basic pattern of uniform wall thickness, such as the basicpatterns 5 (FIG. 5), is cut off the rest of the sheet 8 by means of aknife or a severing disc, respectively.

As initially mentioned, such a basic pattern 5 can directly be used as acasting pattern, for example, in the manufacture of saddles or dentalplates or ring cover crowns and solid cast crowns, in which cases theanatomic basic form has previously been molded in embedding compound orin a similar manner. If, how ever, an object such as a crown withlocally increased wall thicknesses is to be cast, the additionalthickness, e.g. on the triturating surface, is molded by applying wax toa basic pattern such as the pattern 5.

In order to obviate contraction of the formed basic pattern when this iscooling down, a compensating sheet may be used, as already mentioned,which is so chosen that its thickness corresponds to the contraction ofthe basic pattern to be compensated and preferably also to the finalcasting. Expediently such compensating sheet is also clamped to thesupporting plate 7, that is, on the underside of the pattern sheet, towhich it snugly adheres, and facing the pattern support to be copied.

Thus the compensating sheet is plasticized contemporaneously with thepattern sheet and pressed onto the pattern support. Upon completion ofthe forming operation the compensating sheet, which consists of aplastic that does not combine with the pattern sheet, is elimi* nated.

The sheets are mostly larger than the object to be copied or formed. Toprevent in the non-deformed places between the sheets the presence ofair bubbles which expand during the heating operation and may adverselyaffect accurate forming of the object, it is advantageous to provide thecompensating sheet in the region of the non-deformed places thereof withholes through which the trapped air is allowed to escape.

The apparatus is provided with a pressure regulator in the conduitleading to the blower head 17, whereas the pressure cylinder 16 isdirectly supplied with line pressure. The different switches for theheater 14 and for the compressed air conduits shown only partly in thedrawings may be of any known type and actuable by hand or at least inpart automatically, e.g. in dependence on the position of the rotaryhead 12.

It is to be understood that the heater 14 and the blower head 17 mightas well be angularly displaced from each other through an angle of 90instead of through 180 as illustrated in the drawings. In this case, twooppositely arranged working tables 2 with respective trays 3 might beprovided and operated from the column 11 standing therebetween, therotary head 12 either carrying a heater 14 and a blower head 17, asillustrated, or two pairs of such means arranged opposite each other.Inthe former alternative the two working tables might be used in turnfor carrying out the heating and forming operations, whereas in thelatter alternative these operations could be effected at the same time,using both tables simultaneously.

It is further to be understood that also other details of the device asherein described and illustrated in the accompanying drawings may bemodified analogously within the scope of the invention. For example, onprinciple it is also possible that the heater and the blower head arestationary while the working table is arranged so as to be rotatableinto the two respective working positions.

As already implied, for making the basic casting pattern also a vacuummay be used instead of compressed air. Finally, if the basic pattern tobe made is of simple geometric internal shape, also a simple mechanicalpress, such as a screw press, may be employed to form the basic dentalcasting pattern.

Be it still noted that the applicatiton of the compensating sheet is notlimited to dentistry and to the hereinbefore described combination ofsuch compensating sheet with a basic or casting pattern made of aplastics sheet, but can also be extended to shrinkage compensation ingeneral.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changeswhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

I claim:

1. A method of making dental castings comprising:

(a) providing a dental die model of at least one tooth form from anindividual,

(b) providing a sheet of thermoplastic material,

(c) heating the sheet to soften the material therein,

((1) conforming the softened sheet to the dental die model to form anaccurate reproduction thereof,

(e) cooling the reproduction to form the thermoplastic material into ashaped, dental casting pattern,

(f) embedding the cooled dental casting pattern in a molding means,

(g) removing the material of the dental casting pattern from the moldingmeans to form a mold cavity therein, and

(h) pouring molten material into the molding means to form a cast dentalarticle in the mold cavity.

2. A method as defined in claim 1 including the step applying wax toform thickened portions on the reproduction after the cooling step forcasting a dental article having variable thicknesses.

3. A method as defined in claim 1 wherein the conforming step includesstretching the softened sheet of thermoplastic material over the dentaldie model by an amount effective to avoid formation of folds therein.

4. A method as defined in claim 1 wherein the conforming step comprisesmechanically pressing the softened sheet over the dental die model.

5. The method as defined in claim 1 wherein the thermoplastic materialis disintegratable at elevated temperatures and the removing stepincludes heating the molding means to disintegrate the thermoplasticmaterial thereby forming said cavity.

6. A method as defined in claim 5 wherein said thermoplastic material isselected from the group consisting of polymethacylates and polyolefines.

' 7. A method as defined in claim 5 wherein the conforming step includeseffecting a different air pressure on each side of the sheet when thesoftened sheet is placed over the die model.

8. A method as defined in claim 7 wherein a positive compressed airpressure is applied on the side of the softened thermoplastic sheetopposite the dental die model to effect the different air pressure oneach side thereof.

9. A method as defined in claim 7 wherein a vacuum is formed on the sameside of the softened thermoplastic sheet as the dental die model toeffect the different air pressure on each side thereof.

10. A method of making dental castings comprising:

(a) providing a dental die model of at least one tooth form from anindividual,

(b) providing a first sheet of thermoplastic material for forming adental casting pattern,

(c) providing a second sheet of thermoplastic material for forming ashrinkage compensating layer between the first sheet and said dental diemodel,

(d) heating the sheets to soften the material therein,

(e) placing the second sheet on the dental die model and then (f)conforming the softened first sheet to the dental die model with thesecond sheet disposed therebetween to form an accurate reproduction ofthe said model,

(g) said second sheet having a thickness effective to compensate for theamount of shrinkage resulting upon the cooling of the firstthermoplastic sheet,

(h) cooling the reproduction to form the thermoplastic material into ashaped, dental casting pattern,

(i) embedding the cooled dental casting pattern in a molding means,

(j) removing the material of the dental castign pattern from the moldingmeans to form a mold cavity therein, and

(k) pouring molten material into the molding means to form a cast dentalarticle in the mold cavity.

11. A method as defined in claim 10 wherein the thermoplastic materialof the first sheet and the thermoplastic material of the secondcompensating sheet do not combine with each other upon heating and thematerial of the second compensating sheet is removed from the cooleddental casting pattern before being embedded in the molding means.

12. A method as defined in claim 11 wherein the second sheet ofthermoplastic material includes openings therein to provide a vent forany trapped gases when the thermoplastic sheets are applied to thedental die model.

13. A method as defined in claim 11 wherein the conforming stepcomprises mechanically pressing the softened sheets over the dental diemodel.

14. A method as defined in claim 11 wherein the thermoplastic materialis disintegratable at elevated temperatures and the removing stepincludes heating the molding means 8 Kelly 264-94 Zimmerman 264-92 Lyman264-.92 Cohen 264-19 Hansen 32-12 Streim 32-12 Baldwin 264-16 Germany.

DONALD J. ARNOLD, Primary Examiner A. H. KOECKERT, Assistant Examiner 7to disintegrate the thermoplastic material of the 2,474,676 first sheetthereby forming said cavity. 2,989,780 15. The method as defined inclaim 14- Wherein 3,021,569 the conforming step includes effecting adifferent air 3,058,216 pressure on each side of the sheet when thesoftened I, 1,456,472 sheet is placed over the die model. 2,219,0583,404,056 References Cited UNITED STATES PATENTS 264,558 1,304,396 /1919Smlth 264-19 1,335,372 3/1920 Fredricks 264-19 1,896,123 2/1933Schweitzer 264-19 2,186,468 1/ 1940 Schwartz 264-19 2,249,890 7/1941Droge 264-19 2,271,454 1/1942 Erdle et a1. 264-19 15 2,391,106 12/1945Saffir 264-19 US. Cl. X.R.

